US3346663A - Process for the production of polyoxymethylenes - Google Patents

Process for the production of polyoxymethylenes Download PDF

Info

Publication number
US3346663A
US3346663A US52051A US5205160A US3346663A US 3346663 A US3346663 A US 3346663A US 52051 A US52051 A US 52051A US 5205160 A US5205160 A US 5205160A US 3346663 A US3346663 A US 3346663A
Authority
US
United States
Prior art keywords
trioxane
polymerization
reaction
copolymer
chain transfer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US52051A
Other languages
English (en)
Inventor
Kern Werner
Jaacks Volker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Evonik Operations GmbH
Original Assignee
Degussa GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Degussa GmbH filed Critical Degussa GmbH
Application granted granted Critical
Publication of US3346663A publication Critical patent/US3346663A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
    • C08G2/38—Block or graft polymers prepared by polymerisation of aldehydes or ketones on to macromolecular compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62M—RIDER PROPULSION OF WHEELED VEHICLES OR SLEDGES; POWERED PROPULSION OF SLEDGES OR SINGLE-TRACK CYCLES; TRANSMISSIONS SPECIALLY ADAPTED FOR SUCH VEHICLES
    • B62M7/00—Motorcycles characterised by position of motor or engine
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
    • C08G2/06—Catalysts
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
    • C08G2/18—Copolymerisation of aldehydes or ketones
    • C08G2/24—Copolymerisation of aldehydes or ketones with acetals

Definitions

  • the present invention relates to a novel process for the production of polyoxymethylenes.
  • One of the objects of the present invention is to produce thermally and chemically stable polyoxymethylenes.
  • Another object of the invention is to use monomeric formaldehyde and/or lower oligomers such as trioxane as the starting material for the production of thermally and chemically stable polyoxymethylenes and copolymerized polyoxymethylenes.
  • a further object of the present invention is to produce polymers and copolymers of formaldehyde and/or lower oligomers such as trioxane having thermal properties which will permit their use in high temperature plastic forming processes.
  • the objects of the present invention are accomplished by polymerizing and copolymerizing formaldehyde and/ or lower oligomers such as trioxane in the presence of compounds having the structural unit at least once in their molecular structures. These compounds, in the present invention, act as chain transfer agents and copolymerizing compounds.
  • the polyoxymethylenes .produced by these prior art processes have molecular weights between 5000 to 500,000 depending upon the special reaction conditions employed in the respective processes. These polymers are thermally and chemically unstable. Analytical tests of these prior art polymers have shown that their chain structures are formed of recurring -CH O units and that the ends of the chains always contain OH groups.
  • the macromolecular polymers depolymerize under various conditions fairly readily and this decomposition of the polymer will occur when the polymer is subjected to one of three different environmental conditions and/ or chemical attacks.
  • THERMAL DECOMPOSITION The first of such conditions :arises when these polymers, containing hydroxylv groups on the ends of their chains, are subjected to a temperature of 150 C. and higher as "Ice would occur when these polymers are being shaped in plastic extrusion or pressing operations. At these temperatures a rapid splitting off of monomeric formaldehyde from one or both ends of the chain occurs in a type of slide fastener or zipper opening reaction, analogous to the thermal decomposition of low molecular weight semi acetals into aldehydes and alcohols, which leads to the decomposition of the entire macromolecule.
  • 2,512,950 discloses the etherification of polyoxymethylenes with alcohols in the presence of sulfuric acid and Belgian Patent 570,884 discloses the etherification of the hydroxyl groups of polyoxymethylenes with aliphatic acetals in acidic solutions.
  • British Patent 770,717 furthermore, discloses the esterification of the hydroxyl groups on the'end of the polyoxymethylene chains with acid anhydrides such as acetic acid anhydride in order to produce thermally stable polyoxymethylenes.
  • British Patent 796,863 discloses a process whereby at least partially heat stable end groups are formed concurrently with the formation of polyoxymethylenes from monomeric formaldehyde in the presence of catalysts by means of a so-called chain transfer agent.
  • the chain transfer principle has been known to the art for some time in regard to, for example, polymerization reactions which proceed according to a radical forming mechanism such as in the case of the polymerization of styrene in the presence of carbon tetrachloride.
  • a radical forming mechanism such as in the case of the polymerization of styrene in the presence of carbon tetrachloride.
  • chloroform acts as a chain transfer agent in the polymerization of ethylene.
  • the auto-oxidative decomposition of polyoXy-methylones can be readily avoided, in a known manner, by the addition of anti-oxidants to the polymer compositions. These anti-oxidants have also been used for stabilizing other polymers for a long time.
  • the objects of the present invention are obtained, generally speaking, as mentioned above, by polymerizing Water free, monomeric formaldehyde and/or oligomers such as trioxane under essentially water free conditions in the presence of catalysts and with the aid of chain transfer agents which contain the structural unit at least once in their structures.
  • Under essentially water free conditions means that the entire reaction system should contain less than 3% water, preferably less than 1% and most preferably less than 0.1%.
  • the catalysts to be used in the present invention are any of those which are known to be usable as formaldehyde and/ or oligomer polymerization catalysts.
  • ionic catalysts such as amines and quaternary phosphonium and ammonium compounds can be used and when polymerizing trioxane type polymers cationic catalysts such as Lewis acids and Friedel-Crafts catalysts can be used.
  • Catalysts of these types are disclosed in the following patents: U.S. 2,828,- 286; German 962,116; German Auslegeschrift 1,037,286 and British Patents 796,862; 793,673; 766,629; 753,299 and 748,836.
  • some of the compounds disclosed herein as chain transfer agents are only used with oligomers such as trioxane while others are used with both monomeric formaldehyde and the oligomers.
  • the chain transfer agents of the present invention fall into three classes, generally.
  • the class I compounds cover those compounds which contain one such structural unit,
  • class I compounds are only used, Within the scope of the present invention, with oligomers such as trioxane.
  • Class II and class III compounds are used with both monomeric formaldehyde and oligomers such as trioxane.
  • the class H compounds include compounds which contain at least one such structural unit,
  • class III compounds include those polymeric materials which contain more than one such structural unit,
  • chain transfer agents can be so supervised that the molecular weight of the polymers produced can be feasibly regulated generally. If relatively high concentrations of these chain transfer agents are used comparatively lower molecular weight polymers are obtained which have .a molecular weight of about 2000. On the other hand if higher concentrations of the chain transfer agents are used polymers are obtained which have a molecular weight of 50,000 or more. However, when class II compounds are used, the quantities of them that are used do not have a critical effect on the molecular weight of the polymers produced because of the particular mechanics of the copolymerization reaction involved.
  • the yields obtained by the process of the present invention are almost entirely dependent upon the duration of the polymerization reaction so that it is conceivably possible to conduct the polymerization until almost quantitative yields are obtained.
  • the polymerization process of the present invention can be conducted in an inert organic solution or it can be conducted as a bulk polymerization process.
  • the solvents that can be used are aliphatic and aromatic hydrocarbons such as benzene, toluene, xylene, cyclohexane, hexane, heptane and petroleum ether.
  • aromatic nitro compounds such as nitrobenzene and halogenated hydrocarbons, in particular chlorinated hydrocarbons, for example, 1,2 ethylene chloride, methylene chloride, etc., but especially those which contain only one chlorine atom, are also very useful as solvents.
  • These solvents can be used alone or in admixture with one another.
  • ethyl ether is the preferred medium.
  • polymerizing trioxane it is preferable to use molten trioxane and conduct a bulk polymerization process.
  • the height of the polymerization temperature has no important influence on the success of the polymeriaztion reaction. At higher temperatures, however, the polymerization reaction will proceed more swiftly. It is also often advantageous to use higher temperatures in order to be able to work with a homogeneous mixture of the reactants.
  • the polymerization reaction of the present invention can be carried out at a temperature between 100 C. and +160 C. Unless otherwise indicated, the reaction temperatures used in the examples disclosed in the present application are room temperatures.
  • polymers produced using other Group I compounds, such as aliphatic ethers and acetals, with trioxane as the starting material will be both thermally and chemically stable.
  • the thermal stability of these latter type polymers containing ether type, acetal end groups are particularly resistant to auto-oxidation type decompositions, even at very high temperatures (over about 170 C.).
  • the resistance of these polymers to auto-oxidation attack can also be further enhanced by the addition thereto of known anti-oxidants such as are used for rubber, polyethylene and polypropylene.
  • trioxane for the production of polyoxymethylenes, rather than monomeric formaldehyde, offers substantial technical advantages since trioxane is a solid material at room temperature and much easier to work with.
  • a further advantage in using trioxane rather than formaldehyde as a starting material is the formers extremely slight Water content.
  • trioxane together with the Group I chain transfer agents of the present invention is also advantageous for the reason that the reactability of trioxane corresponds approximately to that of these Group I chain transfer agents. In this way a better utilization of the amount of the chain transfer agent present during the polymerization reaction results and the chain transfer agent does not have to be used, as is the case when polymerizing monomeric formaldehyde as in British Patent 796,863, in substantially excess quantities with respect to the intended effect.
  • Group I chain transfer agents within the scope of the present invention which contain one structural unit in their structure in a non-cyclic arrangement include:
  • esters of organic acids such as ethyl acetate, methyl benzoate, ethyl propionate, ethyl formate, methyl propionate, isopropyl cinnamate and cyclohexyl valerate; and v (d) Anhydrides of organic acids such as acetic acid anhydride, propionic acid anhydride, benzoic acid anhydride, butyric acid anhydride and cyclohexyl carboxylic acid anhydride.
  • Group I compounds can be used as chain transfer agents either alone or in admixture with one another.
  • the amount of the chain transfer agent to be added to the polymerization system depends upon whatever molecular weight is needed for the polyoxymethylenes in the particular case at hand. In general, 0.001 to 50% by weight based on the amount of trioxane used, of the chain transfer agent can be used in the polymerization system of the present invention. Quantities, however, outside this range can also be used without any undesirable detriment to the polymer produced arising. Any unreacted quantities of the chain transfer agent present in the polyoxymethylenes after the termination of the polymerization reaction can be removed and recovered again therefrom by suitable recovery procedures during the purification of the polymerizate.
  • trioxane type formaldehyde polymers with Group I chain transfer agents can be carried out between l00 and +150 C.
  • the more preferable and advantageous operating temperatures, however, are between 0 and C.
  • this polymerization reaction can be conducted either with or without the use of a solvent.
  • a solventit is preferable to use, in this regard, essentially water free, inert, organic solvents, such as nitrobenzene, methylene chloride, hydrocarbons and the like.
  • the polymerizates are obtained in good yields. They can be purified, where necessary, to free them of lower molecular weight polymer fractions as well as residual quantities of the chain transfer agents and catalysts by washing them and extracting them with methanol and solutions of sodium hydroxide.
  • the molecular weights of the polyoxymethylenes produced using trioxane and Group I chain transfer agents can be varied over a wide range by an appropriate regulation of the quantity of chain transfer agent present during the polymerization reaction. It is thus readily possible, by this procedure, to regulate the softening point of the polymers produced, at will.
  • Example 1 1000 parts by weight of water free trioxane were melted and mixed with 50 parts by weight of di-isopropyl ether. After the addition of 10 parts by weight of antimony pentachloride to this mixture the reactants were transformed almost quantitatively to a polyoxymethylene, which, after having the catalyst (SbCl removed therefrom with an aqueous sodium hydroxide solution and after also adding thereto 2% by Weight of phenyl-flnaphthyl amine, when subjected to a temperature of 180 C. lost only a few parts per thousand in weight per hour. The polyoxymethylene thus obtained was also not altered when treated with alkalies at elevated temperatures and also displayed a substantial stability against acids.
  • the reaction temperature was 70 to 80 C. and the duration of the polymerization was to minutes. The yield was 90%.
  • Example 2 50 parts by weight of water free trioxane and 3 parts by weight of diethyl formal were dissolved in 100 parts by weight of methylene chloride and then 1 part by weight of boron trifluoride etherate was added to the solution. A polyoxymethylene was thus formed, which, after being freed of residual quantities of the catalyst, chain transfer agents and lower molecular weight fractions by treatment with sodium hydroxide solutions and methanol, lost less than 1 part per thousand in weight per hour at a temperature of 180 C.
  • the polymerization reaction temperature was C. and the duration of the reaction was 1 hour. The yield was over 90%.
  • Example 3 9 g. of fractionally distilled ethyl acetate and 100 g. of pure, essentially water free trioxane were dissolved in 200 ml. of essentially water free trioxane at C. 50 ml. of a 10% solution of boron trifluoride etherate in methylene chloride were then added to the former solution with vigorous stirring. After a polymerization time of a half hour the resulting insoluble polyoxymethylene powder was filtered from the reaction solution, Washed with ethyl ether and thoroughly heated in ethyl ether to remove residual traces of the BF initiator.
  • the polymer which was obtained in good yields was mixed With 2% phenyl-B-naphthyl amine and subjected to a thermal decomposition test in the air at 160 C.
  • the test material quickly lost a portion of its weight. However, the remaining 70% (after a few hours at 160 C.) of the polymer only lost about 1% of its weight per day thereafter at 160 C.
  • Example 4 When diethyl phthalate was used instead of ethyl acetate in the reaction conditions of Example 3 a thermally stable polyoxymethylene was obtained which contained phthalate end groups.
  • Example 5 7 g. of freshly distilled acetic acid anhydride, which had been previously freed of the last traces of water and acetic acid by being treated with calcium hydride, were mixed with 200 ml. of essentially water free nitrobenzene and 100 g. of pure trioxane. The polymerization was initiated by the addition of 20 ml. of a 10% solution of boron trifluoride etherate in nitrobenzene and was allowed to continue for 50 minutes at C. with stirring. 80 g. of polyoxymethylene diacetate were obtained by filtering the resulting polymer and washing it with ether.
  • the resulting, white, fine powdery polymer 8 was mixed with 1% by Weight of phenyl-fi-naphthyl amine and tested for its thermal stability by heating it in the air at C. During the first 30 minutes of the test the polymer lost 10% of its Weight whereas for sev eral days thereafter, at the same temperature, it only lost less than 1% of its weight per hour.
  • class II COMPOUNDS are compounds which contain the structural unit at least once in their structure in a cyclic arrangement and which also contain at least one carbon to carbon bond in their hetero cyclic structure. These compounds, in the present invention, can be used as chain transfer agents when both monomeric formaldehyde and oligomers such as trioxane are to be polymerized to form polyoxymethylenes under essentially water free conditions in the presence of a polymerization catalyst.
  • the object of the use of these Group II chain transfer agent in the present invention is to prevent, by means of one polymerization technique, all three of the above described decomposition reactions from affecting the polyoxymethylenes produced thereby, if not completely then at least by limiting the possible effect of these three decomposition reactions to small segments of the polymer chains thereby attacked.
  • the principle involved in the use of these Group II chain transfer agents consists in interrupting the sequence of acetal bonds.
  • the size of the segment of the chains of the polyoxymethylenes of the present invention that will decompose when the chain is subjected to attack, in one of the three described manners, will be inversely proportional to the number of comonorner groupings contained in the copolymer chain, that is, the higher the degree of copolymerization with the copolymer and the more comonomer units there are in the copolymer then the smaller will be the possible degree of decomposition.
  • the analysis of the copolymer produced in Example 11 disclosed a comonomer (4-phenyl-l,3- dioxane) content of only 0.7 mol percent.
  • the copolymer had a molecular weight of about 20,000, which corresponds to a degree of polymerization of about 650, in relation to its CH O unit content.
  • every copolymer chain also contained 4 comonomer units statistically distributed.
  • a thermal decomposition of the chain, from the hydroxyl end groups in would only effect a fourth of the chains length since the rest of the chain would lie between protective comonomer units.
  • the desired mechanical and physical properties of the polyoxymethylenes of the present invention can be obtained by incorporating about 1 mol percent or even less of the comonomer into the copolymer.
  • a comonomer content is normally suflicient for stabilizing the polyoxymethylenes, for certain fields of application as well as for modifying the physical properties of the polyoxymethylenes it can be advantageous to incorporate more of the comonomer units therein, for example, mol percent, and even more.
  • the thus stabilized polyoxymethylenes canbe formed from monomeric formaldehyde as well as from trioxane or from a formaldehyde cleaving polymer of formaldehyde.
  • Cyclic ethers and acetals such as ethylene oxide, propylene oxide, glycide ether, styrene oxide, cyclohexene oxide, tetrahydr-ofurane, 1,3 dioxolane, 1,3 tlioxane, 4-phenyl-l,3-dioxane, 1,3 dioxa cycloheptane, cyclo benzophenone glycol ketal and cyclo cyclohexanone glycol ketal;
  • Cyclic carboxylic acid anhydrides such as phthalic acid anhydride; cyclic adipic acid anhydride, succinic acid anhydride and maleic acid anhydride.
  • Che-mists working with lower molecular weight polymers know, in relation to cyclic compounds of the type listed above,-that these ring structures can be readily opened by means of the ionic mechanics involved in various reactions, for example, by saponification. This is just what happens in the present invention wherein the hetero cyclic compounds are attacked by the growing polyoxymethylene ion and the cyclic structures are opened and are in turn united with the polyoxymethylene chain.
  • This copolymerization reaction of the present inven- ⁇ tion can be carried out as a bulk polymerization reaction process but it is preferably conducted in an inert, organic solvent. It is possible to use monomeric formaldehyde as well as monomeric trioxane as the starting material.
  • the purified, in particular essentially water-free, formaldehyde compound monomers and cyclic compound comonomers can be placed in the reaction vessel all at once or they can be continuously added to the reaction vessel .during the course of the reaction.
  • the ratio of the formaldehyde compound monomers (formaldehyde or trioxane) to the cyclic comonome-rs in the reaction mixture is so regulated that 0.1 to 50 mol percent and preferably 0.5 to 3 mol percent of the cyclic comonomer units are incorporated in the copolymer.
  • the ratio of .oxymethylene units to cyclic comonomer units in the polymer is not identical with the ratio of the monomers in the starting mixture.
  • such materials can be used as ionic polymerization initiators as have found use in the prior art in the homopolymerization of trioxane or formaldehyde.
  • This copolymerization reaction can be conducted in the temperature range of l00 to C.
  • organic solvents it is expedient to conduct the polymerization in the formaldehyde saturated solution at lower temperatures within this range, for example, at about 60 C. It is also possible, however, particularly when using trioxane as the starting material, to work at room temperature .or even at higher temperatures.
  • the solvents contemplated for use in this copolymerization reaction technique are in general essentially water free, organic inert solvents, such as, toluene, nitrobenzene, methylene chloride, or benzine.
  • the formaldehyde or trioxane monomer, purified of water as much as possible, and the cyclic comon omer additives of the present invention can be added to 11 the reaction system, either all at once or continuously during the course of the reaction, with the aid of an inert carrier gas.
  • the recovery of the finished polymerizate follows the usual procedure.
  • the various phases are separated mechanically and then the polymerizate is treated with purifying and washing agents such as aqueous solutions of sodium hydroxide and methyl alcohol. In this way residual quantities of the initiators and unreacted monomers are removed.
  • An additional advantageous stabilizing effect against auto-oxidation can be imparted to the polyoxymethylenes produced by this eopolymerization reaction technique by the use of known anti-oxidants, such as phenyl-B- naphthyl amine, in the polymerization reaction.
  • Example 6 Water free monomeric formaldehyde was produced by the thermal decomposition of tat-polyoxymethylene and was thereafter dissolved in water free toluene at 80 C. To 100 ml. of such a toluene solution containing about 6% formaldehyde, 12 g. of water free styrene oxide were added at 80 C. and then nitrogen containing boron trifluoride was introduced into the solution for 1 minute.
  • the polymerization reaction temperature was -70 to 80 C. and the duration of the polymerization was -15 minutes.
  • Example 7 Three parts trioxane and 1 part tetrahydrofurane were heated together with 0.5 mol percent of antimony trifiuoride for hours in a bomb tube at 100-110 C. In this way almost quantitative yields of a white, crystalline, non-sticky polymer were obtained.
  • This polymer consisted essentially of a thermally stable copolymer of trioxane and tetrahydrofurane, which, after the addition of a trace of phenyl-fl-naphthyl amine thereto, lost less than 1% in weight per hour at 180 C.
  • Example 8 g. of water free trioxane and 2.0 g. of 1,3-dioxolane were dissolved in 50 ml. of methylene chloride.
  • the copolymerization reaction was initiated by the addition of pure, elemental iodine to the solution. After the system had stood at room temperature for 15 hours, 7 g. of the copolymer had formed which was recovered by filtering it from the reaction mixture and then washing and drying it.
  • the melting point of this high molecular weight copolymer of trioxane and dioxolane was determined to be 146 C. When heated to 200 C. in a nitrogen atmosphere 12% of the copolymer quickly decomposed. The remainder was thermally stable and lost only 0.4% in weight per hour at 200 C. in a nitrogen atmosphere.
  • Example 9 8 g. of water free trioxane and 2 g. of B-propiolactone were dissolved in 10 ml. of methylene chloride at 20 C. A dilute solution of boron trifluoride etherate in methylene chloride was then slowly added to the trioxane in solution until the system had become turbid indicating that the copolymen'zation reaction had begun. After the termination of the reaction, the resulting copolymers were recovered by being filtered from the reaction system and were freed of boron trifluoride residues adhering thereto by heating the copolymers in diethyl ether.
  • the melting point of the copolymer thus obtained was about C. It displayed, at much higher temperatures, a very good thermal stability, that is, after an initial, quick decomposition loss of 5% of its weight in the form of unstable portions of the copolymer chains, the remaining portions of the copolymer of trioxane and propiolactone (with 1% by weight of phenyl-fl-naphthyl amine added as an anti-oxidant) displayed a loss of only 0.05% in weight per minute in the air at C.
  • the duration of the polymerization reaction was a few hours.
  • Example 10 38.8 g. of water free trioxane and 6.5 g. of water free styrene oxide were dissolved in 100 ml. of dry nitrobenzene. To this solution, 0.50 mg. of boron trifluoride etherate dissolved in 10 ml. of nitrobenzene were added. A rapid polymerization resulted, which was terminated after a few minutes by the addition of methanol containing water. The resulting copolymers were thoroughly washed and dried. They were white, crystalline copoly mers with a melting point of 153-154 C.
  • the copolymer had a comonomer (styrene oxide) content of 2.7 mols of styrene oxide per 100 mols of CH O.
  • styrene oxide comonomer
  • the copolymer was 70% thermally stable without any further treatment and after the initial losses its loss in weight per hour was less than 0.6% of its weight.
  • trioxane is polymerized under similar conditions in the absence of the comonomer (styrene oxide) a completely thermally unstable polyoxymethylene is obtained.
  • Example 11 42 g. of water free trioxane and 16.8 g. of 4-phenyl- 1,3-dioxane were dissolved in 100 ml. of nitrobenzene. Boron trifluoride etherate was used as the initiator for the polymerization. A copolymer was thus obtained, which after being purified in the usual manner, had a melting point of 158 to 160 C. and contained 0.7 mol percent (based on the copolymers CH O content) of 4-phenyl- 1,3-dioxane. The thermally stable portion of the copoly mer amounted to 75.8% when the copolymer was heated to 200 C. under a nitrogen atmosphere. These stable portions lost less than 0.1% in Weight per hour under the same heating conditions.
  • Example 12 10 g. of 4-phenyl-l,3-dioxane were added to 100 ml. of a water free, 6% solution of formaldehyde in toluene prepared as in Example 6.
  • the polymerization reaction began at -50 C. without the addition of a polymerization initiator. However, the reaction was accelerated a great deal by the addition of a few cc. of a dilute aqueous solution of antimony pentachloride to the reaction system.
  • 6 g. of a white, crystalline copolymer having a melting point of 156 C. was obtained after the usual filtering, washing and drying operations. This copolymer lost about 2% in weight per minute as a result of thermal decomposition when heated to C. under a nitrogen atmosphere.
  • Example 13 10 g. of water free y-butyrolactone were added to 10 ml. of a water free, 6% solution of formaldehyde in toluene, prepared as in Example 6, at a temperature of 60 C. The polymerization reaction began without the addition of an initiator. The resulting copolymer was recovered using the usual filtering, washing and drying steps.
  • Polymeric esters such as polyvinyl acetate, polymethylrnethacrylate, cellulose acetobutyrate, polycarbonates and polyethylene-terephthalate;
  • Example 15 50 parts by weight of water free trioxane and 3 parts by weight of 1,3-dioxa cyclic heptane were dissolved in 100 parts by weight of methylene chloride. One part by weight of boron trifluoride etherate was then added to the solution. A polyoxymethylene copolymer was thus formed, which after being recovered and purified, lost less than 1 part in a thousand in weight per hour at a temperature of C. If, for example, three growing polyoxymethylene chains have been joined, independently and successively, to a Example 16 polymethylmethacrylate molecule, then these three polyv oxymethylene chains will have been 'bonded together Monomeric, gaseous, water free formaldehyde was inthrough the polymethylmethacrylate molecule.
  • Example 17 thereby acting as a principal chain, is always formed when the reactive
  • the copolymer obtained has thermal and chemical sta- C O C bility properties similar to the copolymer produced 1n
  • Example groups of the polymeric chain transfer agent are present Example 18 in the latters' side chains as is the case where the polymeric chain transfer agent is, for example, polymethyl- Monomeric, g Water free formaldehyde Was methacrylate, polyvinyl acetate, cellulose acetobutyrate troduced into a water free solution of 3% by weight glyor olyvinyl isopropyl ether, col formal and 0.5% by weight tr'iethyl-isopropyl-am- If h reactive monium iodide in hexan
  • CLASS III COMPOUNDS 7 I groups are present in the principal chain of p the polymeric chain transfer agent, as in the case of The use of the class III compounds of the present inpolyethylene terephthalate, polycarbonates, polyanhyvention as chain transfer agents in the polymerization of I dride's, polypropylene oxide and the like, then a second trioxane or monomeric formaldehyde results in the fortype (B) of'copolymer is formed, by means of a repeated chain tranfer reaction, which resembles a blocked copolymer as follows:
  • class III compounds as chain transfer agents, which are formed from monomeric formaldehyde or trioxane and a polycyclic chain transfer agent which contains ring shaped groupings.
  • An example of such a polycyclic chain transfer agent is polyvinylbutyral. If this polymeric cyclic acetal is used in the polymerization of the formaldehyde compounds then a cross-linked insoluble and infusable copolymer is obtained.
  • polymers having different degrees of polymerization can be used as the class III chain transfer agents, however, it is advantageous to use such polymers which have a degree of polymerization of at least 10.
  • a copolymeric chain transfer agent can be used, for example, a copolymer of methylmethacrylate and styrene.
  • the polymeric chain transfer agents should not contain any, or at most, only very few, active hydrogen groups :as are present, for example, in carboxyl groups, hydroxyl groups and acid amide groups, otherwise the chain transfer reaction during the trioxane or formaldehyde polymerization will take place with these active hydrogen con- .taining groups and unstable hydroxyl end groups will form on the copolymer chain ends.
  • Either water free trioxane as well as water free formaldehyde can be used as the monomeric formaldehyde compound with the class III chain transfer compounds.
  • the formaldehyde compound monomers can be charged into the reaction vessel all at once or they can be added continuously during the course of the reaction.
  • the mixture ratio of formaldehyde compound monomer to polymeric chain transfer agent can be varied between 1:10 and 1:0.01 parts by weight.
  • reaction temperatures lie between 20 C. and +160 C.
  • temperature to be used as well as the choice of solvent and reagent concentrations are largely determined by the solubility of the polymeric chain transfer agent. It is also advantageous to work under such reaction conditions that the product that is formed either remains in solution or only gradually precipitates out.
  • trioxane or formaldehyde with class III chain transfer agents can be started by initiators known to the art, such as, boron trifiuoride or mineral acids. It is important, however, that the initiator that is used by completely removed from the copolymerizate after the termination of the reaction by processing the reaction product by filtering, Washing with organic solvents and treating it with bases such as sodium bicarbonate solutions or dimethyl formamide.
  • initiators known to the art, such as, boron trifiuoride or mineral acids. It is important, however, that the initiator that is used by completely removed from the copolymerizate after the termination of the reaction by processing the reaction product by filtering, Washing with organic solvents and treating it with bases such as sodium bicarbonate solutions or dimethyl formamide.
  • the duration of the polymerization reaction was 20 minutes.
  • Example 20 20 g. of water free trioxane and 1 g. of polyethylene terephthalate were dissolved in g. of water free nitrobenzene at C. The polymerization reaction was initiated with 120 mg. of boron trifluoride etherate. After a 10 minute reaction period at 130 C. a copolymer was obtained which was recovered by filtering after the reaction system was cooled olf. By a fractional recrystallization of the copolymerizate from hot dimethyl formamide it was determined that no significant quantities of homopolymers were present in the copolymerizate.
  • the copolymer was analysed and found to contain 25% by Weight of polyethylene terephthalate. This fraction had a melting point of 220 to 225 C. When melted, a portion of the grafted copolymer quickly decomposed. The larger portion however, exhibited an excellent thermal stability and was fabricated into mechanically formed bodies of high value.
  • Example 21 4 g. of the polycarbonate of 4,4-dihydroxy phenyl- 2,2-propane and 50 mg. of boron trifiuoride-etherate were dissolved in 80 ml. of water free nitrobenzene. In the course of 15 minutes, at 110 C., 16 g. of water free trioxane were added to this solution. Finally, the entire system was stirred for another 15 minutes at 110 C.
  • Example 22 4 g. of polymethylmethacrylate of intermediate molecular weight, 4 g. of water free trioxane and 100 mg. of boron trifluoride etherate were dissolved in water free nitrobenzene at 110 C. In the course of 20 minutes another 12 g. of trioxane and 100 mg. of boron trifluorideetherate were successively added to the reaction system. After stirring the reaction mixture for another minutes at 110 C., it was cooled and the copolymeric pre cipitate was thoroughly washed with methanol after being recovered by filtration and then heated with ethyl ether and dried.
  • the yield amounted to 1.4 g. of a white, crystalline grafted copolymer, the melting point of which was in the neighborhood of 140 C.
  • Example 23 9.5 g. of water free trioxane and 1.0 g. of polyvinyl acetate were dissolved in 50 ml. of water free toluene. The solution was then heated to 110 C. with stirring and a 10% solution of boron trifluoride etherate in toluene was added thereto dropwise until an advanced polymerization reaction was evidenced by the precipitating copolymer. This copolymer was filtered off, washed with water free methanol and ethyl ether and then dried. The yield of grafted copolymer was 3 g. This copolymer melted at 150 C. with a slight decomposition. A test portion of 200 mg.
  • this grafted copolymer was recrystallized from dimethyl formamide and subjected to thermal decomposition conditions at 190 C. under a nitrogen atmosphere. During the first hour the weight of the copolymer decreased about 85 mg., whereas during the next three hours its weight decreased, in all, about 30 mg.
  • formed bodies can be obtained which are tough and elastic, which are not decomposed by alkalies, which are very stable against acids and which depolymerize only to a trifling extent when heated to 180 C. for one hour.
  • Fillers and/or coloring agents such as glass fibers, mineral wool or preferably highly dispersed, active fillers, such as alkaline carbon black, oxides of metals or metalloids, such as aluminum oxide, titanium oxide, zirconium oxide or silicon dioxide, which were obtained by decomposing volatile compounds of these materials at higher temperatures in an oxidizing or hydrolyzing medium, can also be added to all the polymerizates of the present invention.
  • active fillers such as alkaline carbon black, oxides of metals or metalloids, such as aluminum oxide, titanium oxide, zirconium oxide or silicon dioxide, which were obtained by decomposing volatile compounds of these materials at higher temperatures in an oxidizing or hydrolyzing medium, can also be added to all the polymerizates of the present invention.
  • a process for the production of polyoxymethylenes comprising polymerizing trioxane at a temperature between -20 and +160 C. under essentially water free conditions in the presence of a Lewis acid catalyst and at least one organic compound selected from the group consisting of polyvinyl acetate, polymethyl methacrylate, the polycarbonate of 4,4-dihydroxy phenyl-2,2-propane and polyvinyl butyral, said polymeric compounds having a degree of polymerization of at least 10, the quantity of said organic compound being 0.001 to 50 parts by weight per 100 parts by weight of the trioxane.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Polyoxymethylene Polymers And Polymers With Carbon-To-Carbon Bonds (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
US52051A 1959-08-29 1960-08-26 Process for the production of polyoxymethylenes Expired - Lifetime US3346663A (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DED31399A DE1194145B (de) 1959-08-29 1959-08-29 Verfahren zur Herstellung von Polyoxymethylenen
DED32824A DE1202492B (de) 1959-08-29 1960-03-10 Verfahren zur Herstellung von Copolymerisaten des Trioxans
DED32823A DE1201994B (de) 1959-08-29 1960-03-10 Verfahren zur Herstellung von Polyoxymethylenen
DED0033328 1960-05-13

Publications (1)

Publication Number Publication Date
US3346663A true US3346663A (en) 1967-10-10

Family

ID=27436752

Family Applications (2)

Application Number Title Priority Date Filing Date
US52051A Expired - Lifetime US3346663A (en) 1959-08-29 1960-08-26 Process for the production of polyoxymethylenes
US495666A Expired - Lifetime US3293221A (en) 1959-08-29 1965-10-13 Process for the production of copolymers of formaldehyde or trioxane

Family Applications After (1)

Application Number Title Priority Date Filing Date
US495666A Expired - Lifetime US3293221A (en) 1959-08-29 1965-10-13 Process for the production of copolymers of formaldehyde or trioxane

Country Status (6)

Country Link
US (2) US3346663A (en))
BE (1) BE748517Q (en))
CH (2) CH455291A (en))
DE (4) DE1194145B (en))
GB (2) GB961943A (en))
NL (3) NL109971C (en))

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3418278A (en) * 1965-04-07 1968-12-24 Montedison Spa Copolymers of trioxane with cyclic formal and process for preparing same
US3468848A (en) * 1965-07-08 1969-09-23 Montedison Spa Polyoxymethylene copolymers from trioxane an cyclic ketals
US3501438A (en) * 1966-05-13 1970-03-17 Stanislaw Penczek Process for the production of thermostable trioxane copolymers in form of particles of regular size
US3511764A (en) * 1967-03-23 1970-05-12 Grace W R & Co Crosslinked polyacrylamide foam
US3520851A (en) * 1967-07-20 1970-07-21 Du Pont Formaldehyde copolymerization process
US3626027A (en) * 1967-08-04 1971-12-07 Daicel Ltd Process for producing a graft copolymer composition having a polyether as one component
US3681472A (en) * 1960-10-14 1972-08-01 Celanese Corp Shaped structures
US3684767A (en) * 1969-01-16 1972-08-15 Japan Atomic Energy Res Inst Method for preparing polyoxymethylene
US3872182A (en) * 1972-02-22 1975-03-18 Hoechst Ag Thermoplastic moulding composition on the basis of polyoxymethylene
US4049518A (en) * 1968-02-08 1977-09-20 Japan Atomic Energy Research Institute Multi-step radiation process of producing polyoxymethylenes
US4377667A (en) * 1980-06-13 1983-03-22 Asahi Kasei Kogyo Kabushiki Kaisha Polyacetal and process of producing same
DE3410242A1 (de) * 1983-03-23 1984-09-27 Asahi Kasei Kogyo K.K., Osaka Polyacetal-copolymerisate und verfahren zu ihrer herstellung
US5079330A (en) * 1989-08-09 1992-01-07 Toray Industries, Inc. Polyoxymethylene multi-copolymer and its resin composition
US20120232246A1 (en) * 2008-04-16 2012-09-13 Ticona Gmbh Oxymethylene Polymers, Process for the Preparation Thereof and Use Thereof
US8840976B2 (en) 2010-10-14 2014-09-23 Ticona Llc VOC or compressed gas containment device made from a polyoxymethylene polymer
US8968858B2 (en) 2011-12-30 2015-03-03 Ticona Llc Printable molded articles made from a polyoxymethylene polymer composition
US9005515B2 (en) 2011-04-01 2015-04-14 Ticona Gmbh High impact resistant polyoxymethylene for extrusion blow molding
US20150368396A1 (en) * 2012-12-21 2015-12-24 Bayer Materialscience Ag Functionalized polyoxymethylene block copolymers
US9745467B2 (en) 2012-12-27 2017-08-29 Ticona, Llc Impact modified polyoxymethylene composition and articles made therefrom that are stable when exposed to ultraviolet light

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA959989A (en) * 1970-11-12 1974-12-24 Pierino Radici Method of preparing high molecular weight polyoxymethylenes
DE3147309A1 (de) * 1981-11-28 1983-06-01 Basf Ag, 6700 Ludwigshafen Kontinuierliches verfahren zur herstellung von oxymethylenpolymeren

Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2395265A (en) * 1942-05-20 1946-02-19 Du Pont Preparation of dioxolane polymers
US2449469A (en) * 1944-11-02 1948-09-14 Du Pont Preparation of polyformals
GB796693A (en) * 1955-06-10 1958-06-18 Foster Yates & Thom Ltd Improvements relating to pressure or vacuum vessels
GB807589A (en) * 1955-11-30 1959-01-21 Du Pont Block copolymers of formaldehyde and process for preparing same
US2884561A (en) * 1957-06-17 1959-04-28 Du Mont Allen B Lab Inc Synchronizing signal generator
US2966476A (en) * 1956-07-26 1960-12-27 Du Pont Antioxidant composition for polyoxymethylenes
US2989511A (en) * 1958-12-23 1961-06-20 Celanese Corp Catalytic polymerization of trioxane
US3002952A (en) * 1959-09-22 1961-10-03 Du Pont Initiators for the polymerization of formaldehyde
US3012990A (en) * 1959-03-25 1961-12-12 Celanese Corp Moldable copolymers
US3017389A (en) * 1955-03-18 1962-01-16 Du Pont Process of controlling the molecular weight of linear formaldehyde polymers
US3026299A (en) * 1959-03-26 1962-03-20 Celanese Corp Trioxane copolymers
US3027352A (en) * 1958-02-28 1962-03-27 Celanese Corp Copolymers
US3087913A (en) * 1959-03-11 1963-04-30 Celanese Corp Copolymers of trioxane and vinyl ethers

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2870097A (en) * 1955-07-01 1959-01-20 Du Pont Process for the preparation of polymeric acetals
US3147234A (en) * 1958-02-28 1964-09-01 Celanese Corp Modified oxymethylene polymers
BE591716A (en)) * 1959-06-09
BE618213A (en)) * 1959-07-30
BE624203A (en)) * 1961-10-27

Patent Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2395265A (en) * 1942-05-20 1946-02-19 Du Pont Preparation of dioxolane polymers
US2449469A (en) * 1944-11-02 1948-09-14 Du Pont Preparation of polyformals
US3017389A (en) * 1955-03-18 1962-01-16 Du Pont Process of controlling the molecular weight of linear formaldehyde polymers
GB796693A (en) * 1955-06-10 1958-06-18 Foster Yates & Thom Ltd Improvements relating to pressure or vacuum vessels
GB807589A (en) * 1955-11-30 1959-01-21 Du Pont Block copolymers of formaldehyde and process for preparing same
US2966476A (en) * 1956-07-26 1960-12-27 Du Pont Antioxidant composition for polyoxymethylenes
US2884561A (en) * 1957-06-17 1959-04-28 Du Mont Allen B Lab Inc Synchronizing signal generator
US3027352A (en) * 1958-02-28 1962-03-27 Celanese Corp Copolymers
US2989511A (en) * 1958-12-23 1961-06-20 Celanese Corp Catalytic polymerization of trioxane
US3087913A (en) * 1959-03-11 1963-04-30 Celanese Corp Copolymers of trioxane and vinyl ethers
US3012990A (en) * 1959-03-25 1961-12-12 Celanese Corp Moldable copolymers
US3026299A (en) * 1959-03-26 1962-03-20 Celanese Corp Trioxane copolymers
US3002952A (en) * 1959-09-22 1961-10-03 Du Pont Initiators for the polymerization of formaldehyde

Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3681472A (en) * 1960-10-14 1972-08-01 Celanese Corp Shaped structures
US3418278A (en) * 1965-04-07 1968-12-24 Montedison Spa Copolymers of trioxane with cyclic formal and process for preparing same
US3468848A (en) * 1965-07-08 1969-09-23 Montedison Spa Polyoxymethylene copolymers from trioxane an cyclic ketals
US3501438A (en) * 1966-05-13 1970-03-17 Stanislaw Penczek Process for the production of thermostable trioxane copolymers in form of particles of regular size
US3511764A (en) * 1967-03-23 1970-05-12 Grace W R & Co Crosslinked polyacrylamide foam
US3520851A (en) * 1967-07-20 1970-07-21 Du Pont Formaldehyde copolymerization process
US3626027A (en) * 1967-08-04 1971-12-07 Daicel Ltd Process for producing a graft copolymer composition having a polyether as one component
US4049518A (en) * 1968-02-08 1977-09-20 Japan Atomic Energy Research Institute Multi-step radiation process of producing polyoxymethylenes
US3684767A (en) * 1969-01-16 1972-08-15 Japan Atomic Energy Res Inst Method for preparing polyoxymethylene
US3872182A (en) * 1972-02-22 1975-03-18 Hoechst Ag Thermoplastic moulding composition on the basis of polyoxymethylene
US4377667A (en) * 1980-06-13 1983-03-22 Asahi Kasei Kogyo Kabushiki Kaisha Polyacetal and process of producing same
DE3410242A1 (de) * 1983-03-23 1984-09-27 Asahi Kasei Kogyo K.K., Osaka Polyacetal-copolymerisate und verfahren zu ihrer herstellung
US4535127A (en) * 1983-03-23 1985-08-13 Asahi Kasei Kogyo Kabushiki Kaisha Polyacetal copolymers and process for production thereof
DE3410242C3 (de) * 1983-03-23 1998-12-24 Asahi Chemical Ind Polyacetal-Copolymerisat und Verfahren zu seiner Herstellung
US5079330A (en) * 1989-08-09 1992-01-07 Toray Industries, Inc. Polyoxymethylene multi-copolymer and its resin composition
US20120232246A1 (en) * 2008-04-16 2012-09-13 Ticona Gmbh Oxymethylene Polymers, Process for the Preparation Thereof and Use Thereof
US8742065B2 (en) * 2008-04-16 2014-06-03 Ticona Gmbh Oxymethylene polymers, process for the preparation thereof and use thereof
US8840976B2 (en) 2010-10-14 2014-09-23 Ticona Llc VOC or compressed gas containment device made from a polyoxymethylene polymer
US9005515B2 (en) 2011-04-01 2015-04-14 Ticona Gmbh High impact resistant polyoxymethylene for extrusion blow molding
US8968858B2 (en) 2011-12-30 2015-03-03 Ticona Llc Printable molded articles made from a polyoxymethylene polymer composition
US20150368396A1 (en) * 2012-12-21 2015-12-24 Bayer Materialscience Ag Functionalized polyoxymethylene block copolymers
US9688814B2 (en) * 2012-12-21 2017-06-27 Covestro Deutschland Ag Functionalized polyoxymethylene block copolymers
US9745467B2 (en) 2012-12-27 2017-08-29 Ticona, Llc Impact modified polyoxymethylene composition and articles made therefrom that are stable when exposed to ultraviolet light

Also Published As

Publication number Publication date
BE748517Q (fr) 1970-09-16
US3293221A (en) 1966-12-20
DE1201994B (de) 1965-09-30
DE1745698B2 (de) 1972-11-02
GB961942A (en) 1964-06-24
NL255237A (en)) 1900-01-01
CH455291A (de) 1968-06-28
CH459570A (de) 1968-07-15
DE1202492B (de) 1965-10-07
GB961943A (en) 1964-06-24
NL281592A (en)) 1900-01-01
DE1745698A1 (de) 1970-09-17
DE1194145B (de) 1965-06-03
NL109971C (en)) 1900-01-01

Similar Documents

Publication Publication Date Title
US3346663A (en) Process for the production of polyoxymethylenes
DE4106355A1 (de) Verfahren zur herstellung von polyglyoxylaten
US3864287A (en) Process for polymerizing tetrahydrofuran
US3442864A (en) Formals of norbornane-2,7-diols and copolymers thereof with trioxane
US5344911A (en) Process for producing polyoxymethylene copolymer having reduced amount of unstable terminal groups
US3379655A (en) Polymerisation of cyclic acetals
US4931535A (en) Process for the preparation of acetal polymer or copolymer
US4111912A (en) Process for the manufacture of coarse-granular oxymethylene polymers
US3219725A (en) Segmented oxymethylene block copolymers
US3480590A (en) Polymerisation process
US3281499A (en) Block copolymers containing an interior segment of oxymetehylene polymer and polymers of ethylenically unsaturated monomers as exterior segments
US2794014A (en) Water-soluble heteropolymers of acrylic acid, allyl alcohol, and sulfur dioxide and processes for producing the same
US3875117A (en) Process for imparting stability to polyacetals
US3141864A (en) Process for the production of polymerizates or mixed polymerizates of acrolein and methacrolein
US4956445A (en) Process for the preparation of acetal polymer or copolymer
US3122525A (en) Production of polyoxymethylenes
Matsuzawa et al. Solvent effects on stereoregularity of poly (vinyl trifluoroacetate) obtained by radical polymerization
US3477994A (en) Modified polyoxymethylene
JPH03223322A (ja) ポリアセタール共重合体及びその組成物
US3183212A (en) Production of polyoxymethylenes
US4380610A (en) Polyacetal comb polymers
JP5225529B2 (ja) ポリアセタール共重合体の製造方法
US3397182A (en) Polyoxymethylene-type resins and process for their production
US3193531A (en) Process for the production of high molecular weight polyoxymethylene esters and ethers with a definite degree of polymerisation
US3449267A (en) Process of preparing tetrahydrofuran-3,3 - bis(chloromethyl)oxacyclobutane copolymers